1. Field of the Invention
The present invention generally relates to an antenna, and more particularly, to a planar directional antenna.
2. Description of Related Art
An antenna is one of the most indispensable elements in a wireless communication system and which plays an important role in the performance of the entire system. Generally speaking, antennas can be categorized into isotropic antennas, omnidirectional antennas, and directional antennas according to their directivities. A directional antenna transmits and receives electromagnetic signals in a specific direction therefore can be broadly applied to point-to-point communication stations, or devices with the GPS (global positioning system) function, such as smart phones, personal digital assistants (PDAs), GPS navigators, or notebook computers, etc.
The reconfigurable antennas or smart antennas can replace the conventional directional antennas in actual applications. However, a reconfigurable antenna or a smart antenna usually has multiple antenna elements and requires a relatively complicated and enormous feed and distribution network and switches. Thus, a reconfigurable antenna or a smart antenna usually has higher cost and occupies larger surface area and volume. In addition, because a reconfigurable antenna or a smart antenna needs to interact with a decision-making chip along with the change of the external environment and accordingly adjusts the electrical parameters thereof, it is very complicated to implement a system with the conventional reconfigurable antenna or smart antenna.
Thereby, how to design a directional antenna that has a small volume, a high directivity, and a high applicability has become one of the major subjects in the industry.